The present invention relates to a light emitting diode (LED) module with enhanced dimming properties. In particular, the present invention relates to a LED module comprising two LED strings that are designed to be controlled independently such that a dimming curve of the resulting emitted light is obtained which approaches a planckian dimming curve. The present invention further relates to a lamp comprising such a dimming module.
Incandescent light sources when dimmed, e.g. from 100% to 5% of their intensity, change their color temperature from about 2700K to 1900K. Thereby, the resulting dimming curve of the emitted light ideally follows the planckian curve in the CIE chromaticity diagram as shown by curve 7a in FIGS. 2a and 2b. 
LED lighting devices comprising a wide variety of LEDs or LED modules are well-known in the prior art. Also, dimmable LED devices are known in which the current provided to the LED is varied in order to adjust the intensity of the light emitted by the LEDs of the module. In general, this is obtained by providing a pulse width modulated driving current to the LED to be dimmed.
Changing the color temperature of the light emitted by such a LED lighting device is generally addressed by RGB or similar three to four channel solutions. Thereby, such a lighting device comprises at least three to four LED strings, each comprising different monochromatic LEDs of respectively red, green and blue color, said LEDs being provided with different driving currents.
These solutions however need a sophisticated control respectively driving unit such as for example a several channel pulse width modulation microcontroller.
DE 10 2004 047 766 A1 for example relates to such a RGB lighting device with at least four LED modules, whereby the light of at least two of the four LED modules is suitable for being mixed to white light. Thereby, LEDs of the different LED modules have peak wavelengths of between 455 to 485 nm, 512 to 538 nm, 580 to 594 nm and 608 to 626 nm respectively. A provided control unit is designed for dimming of at least three of the four LED modules. By means of the lighting device white light with a desired correlated color temperature and a high color rendering index is provided.
EP 1 462 711 A1 relates to a white LED that can be modified to freely set a color temperature as well as to improve a color rendering property. Thereby, a correction-color LED or LEDs having a peak wavelength in a specific wavelength region in association with a white LED are provided to make a color temperature-regulable LED which permit the correction of not only a color temperature but also a color rendering property by means of color-mixture of the correction-color LED and the white LED considering the color temperature and a spectrum distribution of the white LED. The color temperature-regulable LED is especially useful as a shadowless operating light, a living room light and a decorative light.